Can nature-based alternatives to seawalls keep the waves at bay?

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Areas across the United States facing a greater risk of flooding due to extreme weather and sea level rise are turning to a strong solution: building a wall.

Related: Seawalls ease property owners’ fears of erosion – but not their neighbours

In Miami, a 20-foot seawall has been proposed. In Charleston, South Carolina, a $1.1 billion plan to build a seawall around the city center is awaiting sign-off from Congress. And in New York City, a 2.5-mile seawall under construction along the coast of lower Manhattan is expected to be completed by 2026.

Seawalls have long been used to protect people and property from coastal flooding.

But by solving one problem in one place, these concrete slabs could cause a myriad of problems elsewhere: researchers warn that seawalls could amplify waves at neighboring beaches and destroy nearby ecosystems. As a result, rather than representing a sure way to achieve flood resilience, these structures may actually open the door to greater climate vulnerability.

But more and more places are using nature-based solutions to protect against floods and storm surges.

“Sea level rise is inevitable,” said Danielle Bissett, director of restoration for the Billion Oyster Project. “We need to allow the shoreline to adapt and be resilient instead of putting up seawalls, which are obstructive.”

In a kayak, Louiza Wise, left, an ecological engineer, and Tyler McCormack, right, a graduate student, work to tie down the

In a kayak, Louiza Wise, left, and Tyler McCormack work to tie down the “Emerald Tutu,” a floating marshland being deployed in East Boston. Photo: Boston Globe/Getty Images

The nonprofit hopes to restore 1 billion oysters to New York Harbor by 2035, in an effort to improve the area’s resilience to flooding.

The organization is also working with Living Breakwater, a nature-based green infrastructure in the works along the coast of Staten Island, to cultivate the region’s shellfish habitat. This $107 million effort to mitigate storm surges through living barriers has installed two breakwaters — a series of rock piles that blunt the waves — off the borough’s coast. A total of eight breakwaters are planned.

“We can’t build one-sided infrastructure anymore,” said Pippa Brashear, project manager for Living Breakwaters. The structure consisting of granite rocks and eco-concrete, together with the biological activity that will attach to and grow out of these structures are meant to work together. “We’re creating something that’s not just a structure that knocks down waves, it’s a structure that supports life,” Brashear said.

Staten Island had experienced at least a foot of erosion a year since the 1970s. “By restoring the reef and the marine life that we’re already seeing moving back into the area, the breakwater not only protects against further erosion, it also dampens the waves,” said Katie Brennan, executive director of the Governor’s Office of Storm Recovery.


Further north, researchers in Boston are experimenting with other alternative routes to rigid infrastructure. “Emerald Tutu”, a system of interwoven floating mats with growing vegetation is being developed to protect urban coastlines from sea level rise and storms.

“We’re not creating a solid barrier, but we’re using a network of these small devices around the coast to achieve wave energy dispersion,” said Julia Hopkins, assistant professor of civil and environmental engineering at Northeastern University.

The first ever American seawall was constructed by the Army Corps of Engineers in 1901 on Jamestown Island in Virginia. Since then, the agency developed its own guidelines, regulations and standards for building hundreds of seawalls along the US coastline. But with the nature-based solutions to storm surges, there is no similar blueprint.

“We need to look beyond traditional civil engineering,” Hopkins said. “We are entering a climate era that is unknown, and we need solutions that are flexible.”

Such solutions vary from coast to coast. In the Chesapeake Bay, for example, mangrove restoration is underway. These trees can provide shelter for marine life and slow down the waves. In Florida, marshes and wetlands play a key role in reducing storm surges. And in California, coastal dunes formed when wet sand washes ashore can become obstacles to the wind that carries the bulk of storm damage.

“Swamps and mangroves and other coastal vegetation do a really good job of preventing erosion and trapping sediment so you don’t erode the edge,” said Chela Zabin, a marine ecologist at the Smithsonian Environmental Research Center who works on oyster reef restoration. on the Living Shoreline project, which stretches along the San Francisco Bay.

Whenever a wave hits something that has some kind of texture and ridges, it causes turbulence, which takes out wave energy and allows fine particles to settle out. “So you get both wave protection and also sediment build-up,” says Zabin.

But not all places are well prepared for a soft defense against flooding. In San Francisco, for example, the downtown is so developed that its natural barriers have eroded over time, and a hard concrete barrier may be needed to protect it.

“You have this highly urbanized area right up against the water and a functioning waterfront, there aren’t many options other than a sea wall or a bulkhead,” says Zabin.

With increasing sea level rise, coastal erosion and ecosystem damage, living shorelines and nature-based approaches are now appearing in various forms across the country.

“I would say that what everyone should strive for is to work equally with nature, not against it, because nature always wins,” Bissett said.

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